smart pot soil calculator

How Much Mix (or Medium) Do I Need?

We are often asked “How much mix (or medium) should I buy to fill my 5 gallon Smart Pot?” Or my 10 gallon? Or my three – 7 gallons and one 30 gallon? Planning ahead for this question will make container gardening much, much easier – and a lot more fun!

Container gardeners need to consider – Should I buy a few bags of mix, or am I putting out enough Smart Pot containers that I should perhaps buy a load of mix?

Depending on the size of your container garden ( find out what size container to use ), you may want to consider buying a load of mix as opposed to buying a large number of 50 pound bags of mix. Many grow or hydroponic stores, landscape supply stores and/or garden stores sell mix in bulk. Some will deliver to your back yard, while others will load the mix into your pick-up at their place. Purchasing mix by the load is almost always less expensive than buying separate smaller bags.

Mix is sold in bulk in Cubic Yards. The minimum amount sold is usually about ¾ of a cubic yard, although this varies depending on the supplier. Multiply the number of Smart Pots you plan to purchase by the cubic yard volume. If the volume of mix needed approaches or exceeds ½ of a cubic yard, you should consider buying in bulk.

Following is an approximate volume chart to help you decide if purchasing mix in bulk is a good idea.

Smart Pot is the leading fabric container for faster producing, healthier plants. Click here to learn more in this Smart Pot blog about how much mix is needed when planting.

Container and Pot Sizes: How Much Soil Do I Need?

Container and growing pots come in a variety of sizes. In the United States nursery and garden centers sell pots by the size in inches and gallons. In the United Kingdom, Europe, and most of the rest of the world containers are sold by the size in centimeters and liters.

There are few standards when it comes to container sizes and volumes. To determine the size of a pot measure across the top from one side to the other to determine how many inches or centimeters it is. However, because some pots are long and others are squat and because the sides of some pots are straight and others are tapered, the volume can vary.

How Much Soil Does a Container Need

When it comes to filling a pot with soil estimating how much soil you need is an approximation. Often the volume of a container is measured in liquid quarts or liters, but, of course, when you purchase soil you are purchasing dry (potting soil is not liquid). A dry quart is equal to about 1⅛ liquid quarts. When deciding how much soil to purchase it’s best to factor soil compression that commonly results from moistening and pressing the soil into the pot. Soil compression can add another 15 to 20 percent dry soil to the container. Also take into consideration that when you transplant a plant from one container to another, you will be moving some soil around the roots of the plant.

Take notes on the pots you have and the soil they require. In short order, you will have a realistic estimate of how much soil you will need to purchase when potting plants.

Container garden on a balcony

Soil for Standard Clay Pots and Plastic Nursery Pots:

This chart will help you translate container sizes for standard clay pots and black nursery pots and give you an approximation of how much soil each will require (again these are dry soil measures):

4 inch pot (10 cm) = 1 pint (0.5L)

5-6 inch pot (13-15 cm) = 1 quart (1L) = 0.03 cu. ft.

7-8 inch pot (18-20 cm) = 1 gallon (4L) = 0.15 cu. ft.

8.5 inch pot (22 cm) = 2 gallon (7.5L) = 0.3 cu. ft.

10 inch pot (25 cm) = 3 gallon (11L) = 0.46 cu. ft.

12 inch pot (30 cm) = 5 gallon (19L) = 0.77 cu. ft.

14 inch pot (36 cm) = 7 gallon (26L) = 1 cu. ft.

16 inch pot (41 cm) = 10 gallon (38L) = 1.5 cu. ft.

18 inch pot (46 cm) = 15 gallon (57L) = 2.3 cu. ft.

24 inch pot (61 cm) = 25 gallon (95L) = 3.8 cu. ft.

30 inch pot (76 cm) = 30 gallon (114L) = 4.6 cu. ft.

Soil for Hanging Baskets

10 inch (25 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

12 inch (30 cm) = 7.9 dry quarts (8.4L) = 0.3 cu. ft.

14 inch (36 cm) = 13.9 dry quarts (15.3L) = 0.5 cu. ft.

Soil for Plant Bowls

8 inch (20 cm) = 1.9 dry quarts (2L) = 0.07 cu. ft.

10 inch (25 cm) = 3.7 dry quarts (4L) = 0.14 cu. ft.

12 inch (30 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

14 inch (36 cm) = 8.4 dry quarts (9.2L) = 0.29 cu. ft.

16 inch (41 cm) = 12.0 dry quarts (13.2L) = 0.46 cu. ft.

18 inch (46 cm) = 18.8 dry quarts (20.7L) = 0.73 cu. ft.

21¾ inch (55 cm) = 31.2 dry quarts (34.3L) = 1.21 cu. ft.

Soil for Oval Planters:

12 inch (30 cm) = 3.8 dry quarts (4.1L) =0.14 cu. ft.

16 inch (41 cm) = 7.3 dry quarts (8L) = 0.28 cu. ft.

20 inch (51 cm) = 9.4 dry quarts (10.3L) = 0.36 cu. ft.

Soil for Square Planters:

12 inch (30 cm) = 11.2 dry quarts (12.3L) = 0.48 cu. ft.

15 inch (38 cm) = 23.0 dry quarts (25.3L) = 0.89 cu. ft.

Soil for Window Boxes:

24 inch (61 cm) = 11.7 dry quarts (12.8L) = 0.45 cu. ft.

30 inch (76 cm) = 15.6 dry quarts (17.1L) = 0.6 cu. ft.

36 inch (91 cm) = 19.7 dry quarts (21.6L) = 0.76 cu. ft.

Soil for Strawberry Pots:

5 gallon = 14 dry quarts (15.4L) = 0.54 cu. ft.

Also of interest:

Reader Interactions


Hi this is Maniraj a research scholar from India I would like to know how to calculate volume of a pot and also what does it mean by 1litre of soil.

A litre of soil is the amount of soil that will fill a litre container which is 10cm x 10cm x 10cm.

Volume of a pot… I have a 9 inch diameter pot in front of me as an example… 9 inch top diameter and 7 inch bottom diameter= average diameter of 8 inches.. Formula is.. “Pi” multiplied by “R squared” Radius squared, then multiply that product by the height… So in my case with a nine inch pot I have Pi (3.14159) times (4×4) or 3.14159 X 16= 50.25 square inches multiplied by 8 inches height equals 402 cubic inches. If you want cubic feet then divide the 402 cubic inches by 1,728 cubic inches per cubic foot and you get .237 cubic feet. The 8 1/2 inch container is listed as being .3 cubic feet; the actual measurement would be about .2 cubic feet.

what is the density of potting soil?

Soil density can be measured in a few ways. The presence of sand, silt, loam and organic matter can vary from one soil sample to another–whether you are measuring garden soil or potting soil. Sometimes soil density may include the effect of moisture on the soil. For gardeners, the most common way to measure soil density (garden soil or potting soil) is the hand test: simply grab a handful of soil and squeeze it into a ball. If the soil crumbles apart into many pieces and will not reform when you squeeze it again, then the soil is uncompacted and dry; this soil might be termed light or friable. Soil that breaks apart into a few large chunks that easily reform when you squeeze them is a sign of uncompacted soil with a good amount of moisture. Compacted soils will not break apart in your hand, but are malleable and plastic-like in their consistency when moist; then are hard and unbreakable by hand when dry; this soil would be termed heavy or dense. Other ways to measure soil density include the Protor test; this test requires that three different layers of soil are placed into a cylindrical tube in sequence. A standardized weight is dropped onto the soil repeatedly and the results are measured. The sample then dries overnight and is weighed in order to measure the moisture content. The Nuclear Density Gauge Test is done with a small device that can be transported between testing sights. It operates by measuring the occurrence of a radioactive isotope in the soil in one of two ways. Either by generating small doses of gamma rays that hit the soil surface and then measuring the backscatter–reflection–of the radiation, or by inserting a probe into the soil which transmits the gamma rays directly. Dense, compacted soils absorb more radiation than uncompacted soils. Nuclear density gauges are an expensive, but accurate, timely and effective means of measuring soil compaction.

With 5kgs of potting mix soil, how many medium sized small sized pots can be filled?

Container and growing pots come in a variety of sizes. In the United States nursery and garden centers sell pots by the size in inches and gallons. In the